But brassero is gnome app... I know that kde apps can't fit on gnome live cd.

Actually there isn't any space left in either the KDE or GNOME live
images regardless of whether it is a KDE app or not. With multi-lib,
they don't even fit a CD for x86_64 architecture. You would have to
remove existing apps or find a way to split them up and remove sub
packages if you need more space.